Sure, very few motives in this case could be classified as "blindingly obvious," but your three options for Adnan's reasoning don't make intuitive sense, lack clear delineation, and look like an example of circular reasoning. #1 doesn't make sense as an explanation - if he's so broken up and concerned about Hae's death, then why does he choose to mock the police for their inability to identify her and use a stock racist joke on top of it all? I personally have a pretty dark sense of comedy and sympathize with gallows humor, but this kind of statement just isn't appropriate for the given circumstance. #2 is additionally bizarre -why would he "pretend" to have knowledge that could potentially implicate him when he has no reason to even speak about any of this? If he's innocent and recognizes he was one of the last people to see Hae alive, then this is the last thing he should ever have been caught saying on record.

We've seen no evidence so far besides Adnan's jailhouse statements that he showed any concern whatsoever about Hae when she vanished - all of her other friends attempted to page/call her during her absence, but Adnan made no effort whatsoever to communicate with her. If one of my friends mysteriously left for longer than 2 or 3 days, then you could be positive that I'd do whatever I could to find them/ensure their safety, but Adnan remained fairly unconcerned for the full duration of Hae's disappearance.

You falsely assume that Adnan was thinking clearly when he made the decision to dump Hae's body. He was probably under the influence immediately after committing the crime, and despite his carefully thought-out plan, he and Jay ended up deviating from it after an unknown element of his scheme went wrong.